In the last few years people have been entering the underwater world in ever increasing numbers for both recreation and work. The underwater environment is a dangerous one, and it is important for a diver to be aware constantly of his or her position relative to other divers and/or to hazardous obstacles. It also is important for a diver to be aware constantly of means by which the diver may escape a hazardous situation, such as to a dive boat or tender. In case of an accident it is especially important to be able to find the stricken diver quickly and, if possible, to communicate with the stricken diver.
Prevailing underwater conditions can make vision-based navigation difficult or impossible due to suspended material in the water or to lack of light (e.g., in deep or night-time dives). These conditions, as well as any of various other conditions that can arise underwater, also can substantially increase the difficulty of communication between divers working underwater. Any means by which a diver can be assisted with situational awareness, especially under unfavorable conditions, would enhance overall diver safety and hence enjoyment of this activity.
Similarly, certain types of activities conventionally are conducted, by persons that are not submerged underwater, under conditions of very low visibility such as a smoke-laden atmosphere, nighttime conditions, spelunking conditions, and the like. These conditions, similarly to unfavorable underwater conditions, can substantially increase the difficulty of communication between persons in these conditions and can seriously compromise situational and positional awareness among persons in such an environment.
Conventional systems for use underwater are unable to provide a diver with the respective locations of other members of a dive group or to provide a person in a dive boat or analogous location with the respective locations of divers of a group being tended by the dive boat. Accordingly, there is a need for improved methods and apparatus by which divers can communicate with each other and/or with an operator in a dive boat. There also is a need for improved methods and apparatus by which a diver can know the respective locations (ranges and bearings) of other divers while underwater. There also is a need for improved methods and apparatus of this general type that can be used for communications and location detection in any of various compromised environmental situations including on land or below ground.